\begin{tikzpicture}[>=Stealth, scale=0.6,
    every node/.style={fill=white, inner sep=1pt},
]
    \draw [->] (-0.5, 0) -- (5.5, 0) node[below=0.2em, xshift=1em] {$x$(千克)};
    \draw [->] (0, -0.5) -- (0, 5) node[left=0.2em]  {$y$(厘米)};
    \draw (0, 0) node [below left=0.3em] {\small $O$};
    \foreach \x in {5, 10, 15, 20} {
        \draw (\x/5, 0.2) -- (\x/5, 0) node[below=0.3em] {$\x$};
    }
    \foreach \y in {5, 10, 15, 20} {
        \draw (0, \y/5) -- (-0.2, \y/5) node[left=0.3em] {$\y$};
    }

    \coordinate (A) at (0, 12/5);
    \coordinate (B) at (15/5, 19.5/5);
    \draw (A) -- (B);
    \draw [fill=black] (A) circle(0.1) node[below right=0.3em] {\small $A$};
    \draw [fill=black] (B) circle(0.1) node[right=0.3em] {\small $B$};
\end{tikzpicture}

